Detect the Python interpreter specified by Bazel

[caseyduquettesc]

In a project that builds with Bazel, the python toolchain dictates the path to the interpreter. It would be nice if the python plugin could use this interpreter instead. Not sure if this would be on the python plugin to identify this or the bazel plugin to somehow set this for the python plugin.

[brettcannon]

"It would be nice if the Python plugin could use this interpreter instead". Do you mean you want us to pick up an interpreter from some Bazel extension, or you want the Bazel extension to use the interpreter as specified in the Python extension?

[caseyduquettesc]

pick up an interpreter from some Bazel extension

This one, sort of. Similar to what the intellij plugin does (not sure it works for python, but I see the metadata generation code for it), I would like to see VS Code use the same python interpreter that is configured in Bazel. The java toolchain IDE info is probably more relevant. The idea is to do something similar, but for python. Bazel's python toolchain knows the path to the interpreter to use for the build, so we'd have to somehow get that path over to vscode-python.

For people using the default toolchain, there likely won't be much difference except site-package resolution would work much better (currently I have to double install dependencies, once in bazel and once in a virtualenv I create just for the sake of vscode-python).

There would be a huge benefit though to users doing something like https://thundergolfer.com/bazel/python/2021/06/25/a-basic-python-bazel-toolchain and providing their own python toolchain for hermetic builds. Creating a virtualenv from that just for vscode-python is kind of tricky. Bazel creates an output directory in the project folder which will have symlinks to the python runfiles. I don't know how to systematically get that information besides how the intellij plugin is doing it through aspects.

[brettcannon]

Moved to #17177